Synergy of Plant-Produced Enzymes to Convert Forest Products into Biofuels

Biofuels in the US consist almost entirely of grain ethanol from corn. This has created concern in that a competition for grain for feed and fuel can cause an increase in price which in turn can limit the potential for its use. At best, corn can only account for 25% of replacement fuels. To meet the increasing demand for ethanol, the lowest cost and largest reservoir of plant-based renewable resources lies in the recovery of 5 and 6 carbon sugars from plant cell walls. Cellulosic feedstocks can be derived from either forest or agricultural products. Forest products can account for over 368 million tons or approximately 30% of the estimated available biomass for ethanol production. This requires that plant cell wall polymers be converted into fermentable sugars. The inability to perform this conversion in an efficient and economically viable fashion has limited the commercialization of this technology. One of the major limiting factors toward commercialization is the high cost of enzymes to convert lignocellulosic biomass to fermentable sugars as well as the enormously high capital cost to construct fermentor capacity for the extremely large volumes required. Plant-produced enzymes can be used to overcome the cost and fermentor capacity burden dilemma using microbial-produced enzymes. In comparison with the fermentor capacity capital investment cost of over $200 billion for forest products, obtaining the enzymes from corn germ can be done with existing facilities and minimal capital. Our strategy is to capitalize on our two previous and ongoing efforts: 1) to overproduce cellulase in corn germ, a current agricultural by-product in grain ethanol and 2) to enhance the release of free sugars from cellulosic substrates based on our recent finding that corn extracts can act synergistically with microbial-produced enzymes. These enhancers from plant extracts can significantly lower the enzyme load to deconstruct forest biomass. We will use both transgenic and non-transgenic versions of our enhancer product and quantify the amount that is needed to reduce the microbial enzyme load. We will develop detailed comparisons using cost models showing the reduction in the overall process of ethanol. The successful introduction of this product can enable the use of waste and by-products to be used to produce ethanol or other fermentable products. This would: 1) use existing forest waste and by-products for the source of ethanol rather than require additional inputs for specialty energy crops, 2) decrease fermentor capacity required to produce the enzymes used in this process lowering the upfront capital burden as well as environmental stress, 3) develop a new product from current by-products thereby adding value with no additional input costs, and 4) reduce the overall cost of production of ethanol from forest products to enable it as a competitive alternative for biofuels.